LIFE HISTORY OI- A 1'KRN 3 



embryo, and the embryo matures into an adult. By a 

 series of more or less complicated processes the adult 

 eventually gives rise to another egg, like the one from 

 which it came, thus completing one life-cycle and initiat- 

 ing another. These various changes constitute the life 



FIG. 4. Tree ferns on the military road between Cayey and Caguas, 

 Porto Rico. (Photo by M. A. Howe.) 



history of the individual. The various stages of life 

 history common to most plants are nowhere more clearly 

 illustrated than in the ferns. 



2. Description of a Fern Plant. The more common 

 ferns of temperate regions have underground stems or 

 rhizomes (sometimes called root-stocks), so that only the 



